The visible parts of the human eye 10, as shown in prior art FIG. 1, include the transparent cornea 12, the normally white sclera 14, the colored (blue, green, brown or a mixture of these) iris 16, and an opening in the iris, the normally black pupil. A ray of light, after passing through the cornea 12, which partially focuses the image, passes through the anterior chamber, the pupil, the lens 18, which focuses the image further, the vitreous and is then focused on the retina 20. The retina 20 is a very thin layer of tissue that lines the inner part of the eye 10. The retina 20 is responsible for capturing the light rays that enter the eye 10. The retina 20 is supported by its retinal pigment epithelium, which is normally opaque, the choroid and the sclera. The blood supply of the retina 20 is primarily through the choroid and secondarily through the retinal vasculature 22 which lies on top of the retina 20. The macula 24 is located roughly in the center of the retina 20, temporal to the optic nerve 26. The macula 24 is a small and highly sensitive part of the retina 20 responsible for detailed central vision. The light rays captured by retina are turned into impulses, and the impulses are transported to the brain via the optic nerve 24.
Retinopathy of prematurity (ROP) occurs in over 16% of all premature births. In babies weighing less than 1,700 grams at birth, over 50% will develop ROP. In the United States, over 2,100 children annually experience the complications of ROP, and of which 500 to 1,200 cases of new blindness or severe complications are reported. Studies have found that about 30% of infants with advanced ROP have 20/200 or less in their better eye.
It is known that the retinal area without adequate blood supply emits a chemical trigger (vascular endothelial growth factor) to stimulate growth of the abnormal vasculature. The abnormal vasculature leads to a formation of a ring of scare tissue attached to both the retina and the vitreous gel that fills the center of our eyes. As the scar contracts, it may pull on the retinal creating a retinal detachment.
In 1984, an international classification system was developed that classifies ROP by anatomical zones, clock dial like locations within the eye, and stages of severity. Zone 1 is the posterior of the retina while zone 3 is the far peripheral retina. The larger the number of clock hours of vessels ending in Zone 1, the higher the risk of blindness associated with ROP. Stage 0 is the mildest form of ROP while Stage 5 is the most severe indicating total retinal detachment. FIG. 2 depicts the zones used in the classification and the thresholds for treatment of ROP. Based on classification of the location and extent of the ROP a treatment regime may be prescribed.
Currently, the diagnosis of a patient's ROP condition using the classification system is a manual process that requires subjective judgments. It has been shown that manual designation of the zone 1 boundary varies considerably, while clinicians are generally accurate in identifying the location of the optic nerve and the center of the macula. The inaccurate determination of the extent of the zone 1 boundary leads less than optimal treatment selections.
Thus, while there have been many advances in the diagnosis and evaluation of diseases of the eye, there still exists a need for improved systems and methods that increase the diagnostic accuracy of the conditions, while removing the subjectivity of a physician evaluation.